1. Field Of The Invention:
This invention relates to a universal joint yoke and an associated method and more specifically to a universal joint yoke which is formed by a vacuum die casting process and which is configured to function efficiently as a torque transmitting device.
2. Background Information:
A universal joint is a well known mechanical device which is capable of transmitting rotation from a first shaft to second shaft that is not collinear with the first shaft. One application for the universal joint is in vehicles such as automobiles. Examples of prior art universal joints are disclosed in U.S. Pat. Nos. 699,904 and 719,411.
A universal joint yoke is a piece that connects to each of the drive shafts. Each yoke consists of a tubular body which has an end for receiving the shaft and another end from which a pair of ears project axially. The ears each define a hole for mounting of a bearing. The two bearings are attached to form the universal joint "cross".
Universal joint yokes have traditionally been made from an assembly of components welded together or machined from forged metal blanks. The disadvantages of the welded yoke are that there is a weakness in the yoke at the welded joint and the high component and labor costs. The disadvantage of the forged yoke is that the material is very expensive and much of it is machined away as scrap. Furthermore, the forgoing process limits the shape of the resulting yoke, thus producing inefficient use of the forged metal.
It has been known to make universal joint yokes from castings, however, these cast yokes had unacceptably high porosity which adversely affected the performance of universal joint yoke. Additionally, because of the high porosity, drive shaft tubes could not be welded to the cast yokes.
The shape of the universal joint yoke is especially important for efficient use of the material of which the yoke is composed. The shape of the yoke also affects the stiffness thereof as well as the distribution of stresses thereon. The strongest forces on the yoke are concentrated at the base portion of the ears where the ear is adjacent to the upper surface of the tubular body. Prior art yokes had flat ears which extended axially from the body, and thus were vulnerable at the junction of the ears and the body to metal fatigue. See, for example, U.S. Pat. No. 4,192,153.
U.S. Pat. No. 4,334,414 discloses a universal joint yoke having ears with a cylindrical outer surface and a cylindrical inner surface. The shape of the ears are inturned towards the rotational axis so that the depth of the bore can be increased. This patent, however, is not concerned with the stiffness of the ears or with the distribution of stresses thereon.
Therefore, despite the prior art universal joint yokes, there remains a need for a universal joint yoke that is shaped to result in more uniform distribution of stresses, has greater stiffness and that is lighter in weight than prior art yokes. There is also a need for a method of making a universal joint yoke which is efficient and cost effective while producing a high quality universal joint yoke.